Formation ofH2-rich iodine-hydrogen compounds at high pressure

Abstract

We have used synchrotron x-ray and Raman spectroscopic studies combined with molecular dynamics to investigate the ${\mathrm{I}}_{2}\ensuremath{-}{\mathrm{H}}_{2}$ system at high pressure. By laser heating the mixture above 25 GPa we synthesized the molecular compound $\mathrm{HI}{({\mathrm{H}}_{2})}_{13}$, with the ${AB}_{13}$ structure type and unusually high volumetric hydrogen content. The isolation of HI molecules by ${({\mathrm{H}}_{2})}_{13}$ supramolecular clusters stabilizes the compound over a remarkable pressure range from 9 to at least 130 GPa. At lower pressures and 300 K another compound, hydrogen diiodane ${\mathrm{H}}_{2}{(\mathrm{HI})}_{2}$, spontaneously forms, being stable up to 12.5 GPa.